Mechanical bearings necessarily involve mechanical contact between the components, leading to well-known problems associated with friction and wear. Repulsive magnetic forces have been utilized in magnetic bearings, for example, to provide a non-contact, low-friction bearing. However, magnetic bearing structures require a design which may become quite complicated; for example, for radial magnetic bearings, it is necessary to maintain the rotating component aligned axially with the non-moving component, such as by providing a second magnetic gap to maintain such alignment. Nevertheless, the use of magnetic forces to provide a non-contact, low-friction bearing avoids the drawbacks attendant to mechanical bearings, thereby providing an attractive alternative.
In any magnetic suspension element that utilizes static magnetic forces between a stationary and a rotating component in a first direction, a stable state of equilibrium against external forces, e.g., gravity, in a second direction cannot exist. In other words, if such a bearing element is designed to be stable against transverse displacements, it will be unstable against axially directed displacements, and vice versa. This instability may be addressed by undesirably complicated and expensive electronic and magnetic control systems or the provision of a second magnetic gap, as mentioned above. U.S. Pat. No. 3,493,274 discloses a magnetic bearing utilizing two magnetic gaps, extending perpendicularly to one another, to keep the moving component in place relative to the non-moving component.